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24.3 Sound perception and music  When you hear a sound, the nerves in your ear respond to more than 15,000 different frequencies at once.  The brain makes sense of complex sound because the ear separates the sound into different frequencies.

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24.3 Sound perception and music  A frequency spectrum shows the amplitudes of different frequencies present in a sound.

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24.3 Sonograms  More information is found in a sonogram which combines three sound variables: 1.frequency, 2.time, and 3.amplitude (loudness).

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24.3 How we hear sound  The parts of the ear work together: 1. When the eardrum vibrates, three small bones transmit the vibrations to the cochlea. 2. The vibrations make waves inside the cochlea, which vibrates nerves in the spiral. 3. Each part of the spiral is sensitive to a different frequency.

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24.3 Sound protection  Listening to loud sounds for a long time causes the hairs on the nerves in the cochlea to weaken or break off resulting in permanent damage.

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24.3 Music  The pitch of a sound is how high or low we hear its frequency.  Rhythm is a regular time pattern in a series of sounds.  Music is a combination of sound and rhythm that we find pleasant.

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24.3 The musical scale  Most of the music you listen to is created from a pattern of frequencies called a musical scale.

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24.3 Superposition  The superposition principle states that when sound waves occur at the same time they combine to make a complex wave.  When two frequencies of sound are not exactly equal in value, the loudness of the total sound seems to oscillate or beat.

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24.3 Music and notes  Each frequency in the scale is called a note.  The C major musical scale that starts on the note C (262 Hz).

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24.3 Music and harmony  Harmony is the study of how sounds work together to create effects desired by the composer.  The tense, dramatic sound track of a horror movie is a vital part of the audience’s experience.  Harmony is based on the frequency relationships of the musical scale.

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24.3 Music and harmony  When we hear more than one frequency of sound and the combination sounds pleasant, we call it consonance.  When the combination sounds unsettling, we call it dissonance.

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24.3 Making sounds  The human voice is complex sound that starts in the larynx, at the top of your windpipe.  The sound is changed by passing over by expandable folds (vocal cords) and through openings in the throat and mouth.

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24.3 Making sounds  For a guitar in standard tuning, the heaviest string has a natural frequency of 82 Hz and the lightest a frequency of 330 Hz.  Tightening a string raises its natural frequency and loosening lowers it.

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24.3 Harmonics and music  The same note sounds different when played on different instruments.  Suppose you compare the note C (262 Hz) played on a guitar and the same note played on a piano.  The variation comes from the harmonics in complex sound.  A single C note from a grand piano might include 20 or more different harmonics.

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24.3 Harmonics and music  A tuning fork is a useful tool for tuning an instrument because it produces a single frequency

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Investigation 24C  Key Question:  What is sound and how do we hear it?? Perceiving Sound

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Hearing  Deafness is poorly understood in general. For instance, there is a common misconception that deaf people live in a world of silence. To understand the nature of deafness, first one has to understand the nature of hearing.